Digital Elevation Model

A simple library for accessing elevation values from provided latitude & longitude using the DEM data of the particular area.

Project Setup (CMake)

Prerequisites

1. CMake (version 3.25 or above)
2. C++ compiler with support for C++ 20 standard (or above)

# CMakeLists.txt (at the root of your project)

cmake_minimum_required(VERSION 3.25)
project(Test LANGUAGES C CXX)

set(CMAKE_CXX_STANDARD 20) # C++ standard 20 or above
set(CMAKE_CXX_STANDARD_REQUIRED ON)

# including the downloaded DEM library (<project_root>/external/DEM)
add_subdirectory(external/DEM)

add_executable(${PROJECT_NAME} main.cpp)
target_include_directories(${PROJECT_NAME} PUBLIC ${LIBDEM_INCLUDE_DIRECTORIES}) # include DEM headers
target_link_libraries(${PROJECT_NAME} PUBLIC DEM) # links DEM

Setting up DEM data

1. DEM data of the particular area should be available in any supported standard format. The latitude & longitude bounds of the DEM data should be known.
   e.g. DEM data available from Bhuvan NRSC - Cartosat -1 : CartoDEM Version-3 R1

2. The downloaded DEM data should be converted to a readable text file using a viable GIS tool as per the guidelines of the DEM data provider or the metadata from the downloaded DEM itself.
   e.g.: QGIS can be used to convert the downloaded *.tiff DEM data to ASCII text file format i.e. produces a *.asc file

3. The text based DEM data should be converted to binary file by using the library.

   #inculde "DEM/Utility.hpp"
   
   int main() {
       // creates the `*.bin` file at the same directory as that of the `*.asc` file.
       Utility<int16_t, std::endian::big>::create_dem_asc_bin("./14_76.asc");
       // Utility<datatype = int16_t, endiannnes = std::endian::big> : writes 2 byte signed integer
       // values with big-endian (endianness = std::endian::big) byte order
       // (default: endianness = std::endian::native)
   
       return 0;
   }

DEM Operations

1. The different parameters of the downloaded DEM data should be known (also available after conversion to ASCII representation) :

   • Rows - number of rows in DEM data
   • Columns - number of columns in DEM data
   • Lower Left Corner Latitude - bottom left latitude of the DEM data
   • Lower Left Corner Longitude - bottom left longitude of the DEM data
   • Cell Size - distance (in radians) between every DEM values
   • No Data Value - invalid DEM value representation

2. File path to the created DEM data binary file (e.g. "/home/user/DEM/14_76.bin")

   #include "DEM/DEM.hpp"
   
   int main() {
       // DEM<datatype = int16_t, endiannnes = std::endian::big> : writes 2 byte signed integer
       // values with big-endian (endianness = std::endian::big) byte order
       // (default: endianness = std::endian::native)
   
       DEM<int16_t, std::endian::big>::Type type = DEM::Type(3600, 3600, 14, 76, 0.000277777, INT16_MIN); // nrows, ncols, yllcorner, xllcorner, cellsize, nodata
   
       // the byte order of the '*.bin' file should be known
       DEM<int16_t, std::endian::big> dem(type, "/home/user/DEM/14_76.bin"); // initialise
   
       return 0;
   }

Operations

1. Altitude : returns the DEM height of the given coordinate as the type as in DEM data

   float Latitude = 14.6705686, Longitude = 76.5106390;
   
   auto altitude = dem.altitude(Latitude, Longitude);
   std::cout << "Height :" << altitude << std::endl;

2. Interpolated Altitude : returns the interpolated DEM height of the given coordinate

   float Latitude = 14.6705686, Longitude = 76.5106390;
   
   float interpolated_altitude = dem.interpolated_altitude(Latitude, Longitude);
   std::cout << "Interpolated Height : " << interpolated_altitude << std::endl;

Utility Operations

These functions converts files to the following formats and saves them in the same directory as that of the input files :

• .asc (text file representation of DEM generated from a GIS application)
• .bin (file containing DEM data represented in binary format)
• .csv (comma seperated text file representation of the DEM data for usage with spreadsheets)

1. .asc to .bin : converts .asc (text) file to .bin (binary) file

   Utility<int16_t, std::endian::big>::create_dem_asc_bin("./14_76.asc");

2. .asc to .csv : converts .asc (text) file to .csv (comma seperated values) file

   Utility<int16_t, std::endian::big>::create_dem_asc_csv("./14_76.asc", type);

3. .bin to .csv : converts .bin (binary) file to .csv (comma seperated values) file

   Utility<int16_t, std::endian::big>::create_dem_bin_csv("./14_76.bin", type);

4. .csv to .bin : converts .csv (comma seperated values) file to .bin (binary) file

   Utility<int16_t, std::endian::big>::create_dem_csv_bin("./14_76.csv");

Usage

// main.cpp
#include "DEM/DEM.hpp"

int main() {
    DEM<int16_t, std::endian::big>::Type type = DEM::Type(3600, 3600, 14, 76, 0.000277777, INT16_MIN); // nrows, ncols, yllcorner, xllcorner, cellsize, nodata
    DEM<int16_t, std::endian::big> dem = DEM(type, "/home/user/DEM/14_76.bin"); // initialise

    return 0;
}

Map Operations

Creates a grid of DEM data which can be dynamically loaded into memory at runtime when accessing a coordinate which is not bounded by the currently loaded DEM data.

1. Create a mapping of DEM files to coordinates.

   #include "DEM/Map.hpp"
   
   int main() {
       // Map<datatype = int16_t, endiannnes = std::endian::big> : writes 2 byte signed integer
       // values with big-endian (endianness = std::endian::big) byte order
       // (default: endianness = std::endian::native)
   
       Map<int16_t, std::endian::big>::Grid grid;
       grid[{14, 76}] = {{3600, 3600, 14, 76, 0.000277777, INT16_MIN}, "/home/user/DEM/14_76.bin"};
       grid[{14, 77}] = {{3600, 3600, 14, 77, 0.000277777, INT16_MIN}, "/home/user/DEM/14_77.bin"};
       grid[{14, 78}] = {{3600, 3600, 14, 78, 0.000277777, INT16_MIN}, "/home/user/DEM/14_77.bin"};
   
       Map<int16_t, std::endian::big> map(grid); // initialise
   
       return 0;
   }

   OR, dynamically create grid from DEM files in a directory
   _(NOTE : all the DEM files in the directory must conform to <latitude>_<longitude>.bin file name and must have same properties (nrows, ncols, cellsize, nodata))_

   #include "DEM/Map.hpp"
   
   int main() {
       Map<int16_t, std::endian::big>::Grid grid = Map<int16_t, true>::initialize("/home/user/DEM/", 3600, 3600, 0.00027777, INT16_MIN); // `/` (`\\` in Windows) required at end of the directory path
   
       Map<int16_t, std::endian::big> map(grid); // initialise
   
       return 0;
   }

Operations

1. Altitude : returns the DEM height of the given coordinate as the type as in DEM data

   float Latitude = 14.6705686, Longitude = 76.5106390;
   
   auto altitude = map.altitude(Latitude, Longitude);
   std::cout << "Height :" << altitude << std::endl;

2. Interpolated Altitude : returns the interpolated DEM height of the given coordinate

   float Latitude = 14.6705686, Longitude = 76.5106390;
   
   float interpolated_altitude = map.interpolated_altitude(Latitude, Longitude);
   std::cout << "Interpolated Height : " << interpolated_altitude << std::endl;
   ``

MIT License

Copyright (c) 2023 Pritam Halder

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.